1. Field of the Invention
The present invention relates to a semiconductor laser device, and particularly to a semiconductor laser device capable of oscillating light that contains TE-polarized light of higher intensity.
2. Description of the Background Art
Semiconductor laser devices that oscillate in the TM (Transverse Magnetic) polarization (polarized light having an electric field vector normal to the active layer) include that described in U.S. Pat. No. 5,438,584 (hereinafter referred to as Patent Document 1). The semiconductor laser device of the Patent Document 1 has a structure of layers stacked between an n-electrode and a p-electrode as shown below.
That is to say, the stacked layers include an n-electrode, an n-GaAs substrate, an n-AlGaAs cladding layer, an (AlGa)0.5In0.5P guide layer, a GaAsP active layer, an (AlGa)0.5In0.5P guide layer, a p-AlGaAs cladding layer, an n-GaAs current confining layer, a p-GaAs contact layer, and a p-electrode.
The GaAsP active layer has tensile strain and the GaAsP active layer oscillates TM-polarized light of 600 nm or more.
Now, it is difficult to produce rods or optical fibers that are specially adapted for the TM-polarization. However, passing TM-polarized light into rods or optical fibers adapted for the TE (Transverse Electric) polarization (polarized light having an electric field vector parallel to the active layer) results in deteriorated excitation efficiency.
A device that changes the polarizing angle (i.e., a device that transforms TM-polarized light into TE-polarized light) may be interposed between a semiconductor laser device emitting TM-polarized light and a rod etc., but this involves complicated device structure.
Because of these reasons, semiconductor laser devices that emit TE-polarized light are more practical than semiconductor laser devices that emit TM-polarized light. Also, it is known that increasing the light intensity of TE-polarized light tends to enhance the practicability of the semiconductor laser devices.
A semiconductor laser device capable of emitting light including TE-polarized light of high intensity is described in K. Shigihara et al., “High Power 980 nm Ridge Waveguide Laser Diodes Consisting of Expanded Optical Field Normal to The Active Layer”, IEEE J. Quantum Electron, Vol. 38, No. 8, pp. 1081-1088, August 2002 (which is hereinafter referred to as Non-Patent Document 1).
As above, there are conventional semiconductor laser devices that are capable of emitting light including TE-polarized light of high intensity. However, there are demands for semiconductor laser devices that adopt other structures and are capable of emitting light having such high TE-polarized light intensity as to be suitable for practical use.